ENERGY

Question 1

what is power?

Answer 1

power is the rate of energy transfer

Question 2

unit of power

Answer 2

Watts (W)

Question 3

Equation for power

Answer 3

P= E/T

Question 4

Equation for efficiency

Answer 4

Efficiency= useful energy or power output/ total energy or power output (x100) to turn into a percentage

Question 5

What is efficiency

Answer 5

Efficiency is the proportion/ ratio of TOTAL INPUT energy/power that is converted to USEFUL OUTPUT energy

Question 6

How is thermal energy usually lost

Answer 6

usually lost from buildings through conduction

Question 7

INSULATION PRACTICAL STEPS

Answer 7

1) pour hot water into can/beaker, start timer when temperature falls to chosen initial temp
2) after set time, measure final temp
3) repeat with different types of insulation around can/beaker of different layers of the same insulation

Question 8

Kinetic energy equation

Answer 8

E= 1/2 mv2

Question 9

Gravitational potential energy equation

Answer 9

E=mgh

Question 10

Elastic potential energy

Answer 10

E= 1/2 ke2

Question 11

Thermal energy (SHC) equation

Answer 11

change E= mc change t

Question 12

ENERGY SOURCES - finite/ non renewable sources

Answer 12

• fossil fuels (coal, oil and natural gas) burned to produce heat, often to produce steam to drive turbines and generators
• nuclear fuel used in nuclear reactions to produce heat

Question 13

ENERGY SOURCES - renewable sources (can be replaced)

Answer 13

• wind power -wind has kinetic energy, used to turn turbines
  -hydroelectric- water behind dam has GPE, falls through turbine
• solar power - light from sun produces electricity

Question 14

SHC PRACTICAL STEPS

Answer 14

1) measure mass of metal block or water in beaker, using top-pan balance
2) place electrical heater in metal block/ water
3) measure initial temp of substance using thermometer
4) turn heater on, start timer and measure p.d and current supplied to heater using voltmeter and ammeter
5) after set time, measure final temp and calculate change in temperature

Question 15

What is SHC

Answer 15

the energy required to raise the temperature of 1kg of a substance by 1’c

Question 16

What will happen to the SHC at the end of the experiment?

Answer 16

as energy is lost to surroundings, temp change will be less, so SHC will probably be higher

Question 17

energy is always ______

Answer 17

conserved

Question 18

energy cannot be ______________

Answer 18

created or destroyed

Question 19

What is energy measured in

Answer 19

Joules (J)

Question 20

ENERGY TRANSFERS

Answer 20

things happen when objects interact (in what we call a system) and energy is transferred from one store to another, or between objects

Question 21

In a closed system, ________

Answer 21

no energy is transferred from one store to another, or between objects

Question 22

a system is NOT closed if ____

Answer 22

energy can be lost to the surroundings

Question 23

SHC PRACTICAL how do you calculate power supplied to the block

Answer 23

P=VI (p.d x current)

Question 24

SHC PRACTICAL how do you calculate the energy supplied to the block

Answer 24

E=Pt (power x time)

Question 25

SHC PRACTICAL example apparatus

Answer 25

Joulemeter - measures energy going into the heater in joules (J)
Heater - heats the block
Insulation - stops heating escaping into the atmosphere
Thermometer - measures the temp rise

Question 26

SHC PRACTICAL why do you need to insulate the block

Answer 26

to stop heat loss to the atmosphere

Question 27

SHC PRACTICAL why is your answer not the true value

Answer 27

because not all heat was transferred into the block and through to the thermometer

Question 28

SHC PRACTICAL why is the temperature increase slower at first

Answer 28

because it takes some time for the block to heat up and for the heat to reach the thermometer